Week 3 Flashcards
If you are looking at a wiggly line what is the wavelengths?
the difference in distance between the peaks
What is an example of a long and a short wavelength?
Long - radio/microwave - size of a building-butterfly
Short- Gamma ray or x-ray - size of atmoic nuclei-atoms
What is the colour relationship for long and short wavelengths?
Only a small visible range
What is the relationship between temperature and wavelength
cooler objects emit longer wavelenths, hotter objects emit shorter wavelengths
What kind of radiation can penetrate the earths atmosphere and what is in the grey and what can;t
CAN
Radio and infrared-visible
MAYBE
Some radio and some infrared
CANNOT
microwave and vible-gamaray short wave
What is Planck’s law
Hotter objects emit more radiation - higher specific spectral emittance
hotter objects emit short wave radiation and more radiation overall
the peak wavelength at which objects emit decreases with increasing temperature
What does the sun emit?
the peak is in the visible part of the spectrum
What kind of wavelength does the earth emit
the earth is colder the sun, emits in the infrared part of the spectrum
what percentage of the suns energy does the earth absorb and reflect?
70% absored
30% relected- espeically by light surfaces like clouds, snow and deserts
What is the unit of mesurement for radiative fluxes
W/m^2
the flow of energy through a given surface area over a certain amount of time
What is the global-mean incoming solar radiation and what is the net-absorbed solar radiation
global-mean incoming solar radaition = 340W/M^2
net-absorbed solar radiation is 240w/m^2
What is a radiative balance and how is it achieved?
energy in= energy out
emissions of infrared radiation to space
Without the atmosphere what temperature would the earth be?
-19oc
Without the ghg effect whast would the earth temperature be?
15oc
What is the Co2 content of the atmosphere for Earth and Venus?
.02% = earth
96% Venus
What is the ghg effect?
radiation emitted by earth is trapped by gases in the atmosphere and re-emitted in all directions
when it is re-emitted down this is the greenhouse effect
the large up and down longwave fluxes
idea that there is an asymmetry between absorption by ghg of infrared and visible radiation- traps infra-red
What is albedo?
the reflection of solar energy depends on the albedo the earth atmosphere
high albedo - light reflective surfaces like snow and clouds
low albedo - dark surfaces like water and forests
How do you calculate albedo?
albedo= reflected solar radiation/incoming solar radiation
1= everything is reflected 0= nothing is reflected
What is the earths mean albedo
30%
however this varies spatially and depends on the surface type
Where is shortwave radiation absorbed
mainly at the surface - some in the atmosphere but this is more UV rather than visible
Ozone layer - absorbs harmful carcogenic UV - holes in the ozone due to man-made CFCs
Why are there different amounts of emission from different parts of the atmosphere
due to temperature changes - but what matters is the emissions out to space
typical level that escapes to space has a temperature that corresponds to that emission
What is water vapour opque to?
infrared radiation at many wavelengths - therefore it absorbs it
Why is there so much focus on carbon dioxide
it stays for longer in the atmosphere and thermodynamically unreative - very stable molecule once produced it will remain for a long time
Methane from? and how much in the atmosphere?
gas leaks and livestock
has more than doubled
Where is N2O from?
industrial processes, cars and fertilizers
What does the absoption of radiation by ghg depend on?
the wavelength of infra red radiation
related to the molecular structure of the gases
What is the water vapour window?
a range of wavelengths where eart is able to emit radiation to space.
Co2 is important as it partially masks the water vapour window - a range of wavelengths where the earth is able to emit to space
Increasing CO2 concentration partially close this window
- blocks more of the watervapour window
What are sensible and latent heat fluxes?
Sensible heat is temperature - idea of a direct exchange of heat
Latent heat is humidity - like evaporation requires energy, condensation and then heating.
idea of fluxes by conduction and convection
What does a postive imbalance mean for the earth?
the earth is absorbing more than it emits
the imbalance is mainly due to the strengthening of the greenhouse effect - though there are additional feedbacks
What is radiative forcing?
an externally imposed instantaneous perturbation to the radiative balance - instantaneous perturbation
relative to some reference state it is measured by W/m^2
can be natural such as the sun’s orbit or human such as Co2
can be perturbing the energy in (solar radiation in) or energy out (how much escapes to space)
Can you talk me through how GHG are a radative forcing?
Start in a radiative balance of the same amount of energy going in and out
increase in the amount of GHG means there is in>out - radiative forcing
the earth will accumulate heat thus warm
warming allows the earth to emit more radiative - Plancks Law
this continues until energy out is large enough - then a new equilibrium is reached
Can you give some examples of forcings
Anthropogenic
- aerosol emissions - can reflect or absorb solar radiation
- land use change - surface albedo – contrails from airplanes
Natural
- solar activity variations
- volanic forcings - negative becausing of dimming aerosols -but these are v shortlived 2-3 yrs
From the AR5 report what is the main forcing
Co2
methane and aerosol also have a substantial effect but large uncertainties around aerosols and clouds
What is the effect of aerosols on the atmosphere?
Most have a cooling effectas they directly reflect sunlight or promote the formation of white clouds
however, black carbon has a warming effect as it absorbs sunlight in the atmosphere
there are large regional and temporal differences in aerosol production due to patterns of industry
they don’t mix well in the atmosphere so are quite localised in their effect
If there is suddenly a doubling of the CO2 what would the temperature response look like on a graph?
what about the radiative imbalance line?
Temp
It would be flat until the forcing point then gradually and in a curve warm - and then stablise - initially fsater and then increasingly slowly as it plateus
exponential to begin with then decay to equilibrium
Radiative balance
- sharp increase at forcing point and then a gradual decline to equilibrium
proportional to the temperature change
Plancks law. idea that there is a relationship between temp and wavelength and the net energy emissions -as temperature increases earth radiates more energy and decreases the energy imbalance
what is the energy budget equation ?
Radiative Imbalance = N
Radiative forcing = F (initial forcing)
Radiative response = § (or teepee, trainge T)
N= F-§
What happens if F>0
the earth needs to warm in order to emit more infrared energy to space and re-establish a balance and vice versa (F<0 is a cooling)
Would a postive forcing cool or warm
warming
